Can coupling with remote conduction bands cause a significant normal-incidence absorption in n-type direct-gap semiconductor quantum wells?

Surprisingly, several experiments have reported that normal-incidence light absorption due to interconduction-subband transitions in direct-gap semiconductor quantum wells is as strong as in-plane-incidence absorption. in contrast to other models, a recent theoretical study claimed that a 14-band k . p model including multiband coupling terms due to remote-conduction bands is able to explain the experimental results. in the present work, a concise formulation extends the model beyond 14 bands. Nevertheless, after re-deriving the optical transition matrix elements, this analysis clearly shows that the oscillator strength for the in-plane polarized optical intersubband transition due to the multiband coupling effects is much smaller than the oscillator strength for the normal-to-plane polarized optical intersubband transition. These results indicate that the multiband coupling effects due to remote-conduction bands cannot cause a sufficient in-plane polarized optical intersubband transition to produce the observed normal-incidence absorption in the desirable n-type III-V compound semiconductor quantum wells.